p.Chaos.ImmPhys.Joint.UsePBDDrives
p.Chaos.ImmPhys.Joint.UsePBDDrives
#Overview
name: p.Chaos.ImmPhys.Joint.UsePBDDrives
This variable is created as a Console Variable (cvar).
- type:
Var - help:
Whether to solve drives in the position or velocity phase of the solver (default true)
It is referenced in 4 C++ source files.
#Summary
#Usage in the C++ source code
The purpose of p.Chaos.ImmPhys.Joint.UsePBDDrives is to control whether joint drives are solved in the position or velocity phase of the Chaos physics solver in Unreal Engine 5’s immediate physics simulation.
This setting variable is part of the Chaos physics system, specifically within the immediate physics simulation module. It’s used in the Engine’s physics engine, particularly in the ImmediatePhysicsChaos subsystem.
The value of this variable is set through the console variable system (CVars) in Unreal Engine. It’s defined as an FAutoConsoleVariableRef, which allows it to be changed at runtime through console commands or configuration files.
The variable p.Chaos.ImmPhys.Joint.UsePBDDrives is directly associated with ChaosImmediate_Joint_UsePositionBasedDrives. They share the same value, with ChaosImmediate_Joint_UsePositionBasedDrives being the actual variable used in the code logic.
Developers should be aware that this variable affects the behavior of joint drives in the physics simulation. When set to true (default), it uses position-based dynamics (PBD) for joint drives, solving them in the position phase of the solver. When false, it likely uses a velocity-based approach.
Best practices for using this variable include:
- Understanding the implications of position-based vs. velocity-based solving for joint drives in your specific use case.
- Testing the performance and stability of your physics simulations with both true and false settings.
- Considering the interaction with other joint-related settings, such as SolvePositionLast and EnableDrives.
Regarding the associated variable ChaosImmediate_Joint_UsePositionBasedDrives:
This is an integer variable initialized to 1 (true) by default. It’s used directly in the physics simulation logic to determine whether to use position-based drives for joints. The variable is set through the console variable system and is then used in the FSimulation::Simulate function to configure the JointsSettings.bUsePositionBasedDrives property.
Developers should be aware that changing this variable will directly affect the behavior of joint drives in the immediate physics simulation. It’s important to test thoroughly when modifying this setting, as it can impact the stability and performance of physics-based interactions in the game.
#References in C++ code
#Callsites
This variable is referenced in the following C++ source code:
#Loc: <Workspace>/Engine/Source/Runtime/Engine/Private/PhysicsEngine/ImmediatePhysics/ImmediatePhysicsChaos/ImmediatePhysicsSimulation_Chaos.cpp:117
Scope: file
Source code excerpt:
FAutoConsoleVariableRef CVarChaosImmPhysJointNumShockPropagationIterations(TEXT("p.Chaos.ImmPhys.Joint.NumShockPropagationIterations"), ChaosImmediate_Joint_NumShockPropagationIterations, TEXT("How many iterations to run shock propagation for"));
FAutoConsoleVariableRef CVarChaosImmPhysJointSolvePositionLast(TEXT("p.Chaos.ImmPhys.Joint.SolvePositionLast"), ChaosImmediate_Joint_SolvePositionLast, TEXT("Should we solve joints in position-then-rotation order (false) rotation-then-position order (true, default)"));
FAutoConsoleVariableRef CVarChaosImmPhysJointUsePBDVelocityDrives(TEXT("p.Chaos.ImmPhys.Joint.UsePBDDrives"), ChaosImmediate_Joint_UsePositionBasedDrives, TEXT("Whether to solve drives in the position or velocity phase of the solver (default true)"));
FAutoConsoleVariableRef CVarChaosImmPhysJointEnableTwistLimits(TEXT("p.Chaos.ImmPhys.Joint.EnableTwistLimits"), ChaosImmediate_Joint_EnableTwistLimits, TEXT("EnableTwistLimits."));
FAutoConsoleVariableRef CVarChaosImmPhysJointEnableSwingLimits(TEXT("p.Chaos.ImmPhys.Joint.EnableSwingLimits"), ChaosImmediate_Joint_EnableSwingLimits, TEXT("EnableSwingLimits."));
FAutoConsoleVariableRef CVarChaosImmPhysJointEnableDrives(TEXT("p.Chaos.ImmPhys.Joint.EnableDrives"), ChaosImmediate_Joint_EnableDrives, TEXT("EnableDrives."));
FAutoConsoleVariableRef CVarChaosImmPhysJointLinearProjection(TEXT("p.Chaos.ImmPhys.Joint.LinearProjection"), ChaosImmediate_Joint_LinearProjection, TEXT("6Dof joint projection amount override (if >= 0)."));
FAutoConsoleVariableRef CVarChaosImmPhysJointAngularProjection(TEXT("p.Chaos.ImmPhys.Joint.AngularProjection"), ChaosImmediate_Joint_AngularProjection, TEXT("6Dof joint projection amount override (if >= 0)."));
FAutoConsoleVariableRef CVarChaosImmPhysJointShockPropagation(TEXT("p.Chaos.ImmPhys.Joint.ShockPropagation"), ChaosImmediate_Joint_ShockPropagation, TEXT("6Dof joint shock propagation override (if >= 0)."));
#Associated Variable and Callsites
This variable is associated with another variable named ChaosImmediate_Joint_UsePositionBasedDrives. They share the same value. See the following C++ source code.
#Loc: <Workspace>/Engine/Source/Runtime/Engine/Private/PhysicsEngine/ImmediatePhysics/ImmediatePhysicsChaos/ImmediatePhysicsSimulation_Chaos.cpp:93
Scope: file
Source code excerpt:
int32 ChaosImmediate_Joint_NumShockPropagationIterations = -1;
int32 ChaosImmediate_Joint_SolvePositionLast = 1;
int32 ChaosImmediate_Joint_UsePositionBasedDrives = 1;
int32 ChaosImmediate_Joint_EnableTwistLimits = 1;
int32 ChaosImmediate_Joint_EnableSwingLimits = 1;
int32 ChaosImmediate_Joint_EnableDrives = 1;
Chaos::FRealSingle ChaosImmediate_Joint_LinearProjection = -1.0f;
Chaos::FRealSingle ChaosImmediate_Joint_AngularProjection = -1.0f;
Chaos::FRealSingle ChaosImmediate_Joint_ShockPropagation = -1.0f;
#Loc: <Workspace>/Engine/Source/Runtime/Engine/Private/PhysicsEngine/ImmediatePhysics/ImmediatePhysicsChaos/ImmediatePhysicsSimulation_Chaos.cpp:117
Scope: file
Source code excerpt:
FAutoConsoleVariableRef CVarChaosImmPhysJointNumShockPropagationIterations(TEXT("p.Chaos.ImmPhys.Joint.NumShockPropagationIterations"), ChaosImmediate_Joint_NumShockPropagationIterations, TEXT("How many iterations to run shock propagation for"));
FAutoConsoleVariableRef CVarChaosImmPhysJointSolvePositionLast(TEXT("p.Chaos.ImmPhys.Joint.SolvePositionLast"), ChaosImmediate_Joint_SolvePositionLast, TEXT("Should we solve joints in position-then-rotation order (false) rotation-then-position order (true, default)"));
FAutoConsoleVariableRef CVarChaosImmPhysJointUsePBDVelocityDrives(TEXT("p.Chaos.ImmPhys.Joint.UsePBDDrives"), ChaosImmediate_Joint_UsePositionBasedDrives, TEXT("Whether to solve drives in the position or velocity phase of the solver (default true)"));
FAutoConsoleVariableRef CVarChaosImmPhysJointEnableTwistLimits(TEXT("p.Chaos.ImmPhys.Joint.EnableTwistLimits"), ChaosImmediate_Joint_EnableTwistLimits, TEXT("EnableTwistLimits."));
FAutoConsoleVariableRef CVarChaosImmPhysJointEnableSwingLimits(TEXT("p.Chaos.ImmPhys.Joint.EnableSwingLimits"), ChaosImmediate_Joint_EnableSwingLimits, TEXT("EnableSwingLimits."));
FAutoConsoleVariableRef CVarChaosImmPhysJointEnableDrives(TEXT("p.Chaos.ImmPhys.Joint.EnableDrives"), ChaosImmediate_Joint_EnableDrives, TEXT("EnableDrives."));
FAutoConsoleVariableRef CVarChaosImmPhysJointLinearProjection(TEXT("p.Chaos.ImmPhys.Joint.LinearProjection"), ChaosImmediate_Joint_LinearProjection, TEXT("6Dof joint projection amount override (if >= 0)."));
FAutoConsoleVariableRef CVarChaosImmPhysJointAngularProjection(TEXT("p.Chaos.ImmPhys.Joint.AngularProjection"), ChaosImmediate_Joint_AngularProjection, TEXT("6Dof joint projection amount override (if >= 0)."));
FAutoConsoleVariableRef CVarChaosImmPhysJointShockPropagation(TEXT("p.Chaos.ImmPhys.Joint.ShockPropagation"), ChaosImmediate_Joint_ShockPropagation, TEXT("6Dof joint shock propagation override (if >= 0)."));
#Loc: <Workspace>/Engine/Source/Runtime/Engine/Private/PhysicsEngine/ImmediatePhysics/ImmediatePhysicsChaos/ImmediatePhysicsSimulation_Chaos.cpp:876
Scope (from outer to inner):
file
namespace ImmediatePhysics_Chaos
function void FSimulation::Simulate
Source code excerpt:
JointsSettings.MaxInertiaRatio = ChaosImmediate_Joint_MaxInertiaRatio;
JointsSettings.bSolvePositionLast = ChaosImmediate_Joint_SolvePositionLast != 0;
JointsSettings.bUsePositionBasedDrives = ChaosImmediate_Joint_UsePositionBasedDrives != 0;
JointsSettings.bEnableTwistLimits = ChaosImmediate_Joint_EnableTwistLimits != 0;
JointsSettings.bEnableSwingLimits = ChaosImmediate_Joint_EnableSwingLimits != 0;
JointsSettings.bEnableDrives = ChaosImmediate_Joint_EnableDrives != 0;
JointsSettings.LinearStiffnessOverride = ChaosImmediate_Joint_Stiffness;
JointsSettings.TwistStiffnessOverride = ChaosImmediate_Joint_Stiffness;
JointsSettings.SwingStiffnessOverride = ChaosImmediate_Joint_Stiffness;